The present invention pertains to the compensation of the fanout for affecting the width of a web, which is printed on in the printing press. The present invention pertains to both a fanout compensator and to a process for compensating the fanout. The fanout compensator may already be installed in the printing press or it may also be provided outside the printing press for installation for the purpose of fanout compensation. The printing press is a machine that prints according to the wet method, preferably with the use of a moistening agent. Offset printing shall be mentioned here as an example, in particular. The printing press may be a newspaper printing press for printing large newspaper runs. The web is preferably guided as an endless web through the machine and is wound off from a roll, i.e., the printing press is a web-fed printing press and especially preferably a web-fed rotary printing press in such an embodiment.
Changes occur in lateral expansion in printing presses because of the liquid having penetrated the web. This phenomenon, known as fanout, has the undesired consequence that the width of the web measured at right angles to the direction of conveying of the web changes between two printing gaps in which the web is printed on one after another. Even though the fanout phenomenon may be caused, in principle, by the ink that alone has penetrated, the fanout is significant in practice especially in the case of printing operating with moistening agent because of the moistening of the web which is associated with it. The web moistened in the upstream printing gap along the web swells on its path and becomes wider in the next printing gap of the two printing gaps, which is located downstream along the web. This leads to printer""s errors in the transverse direction of the web unless measures are taken to compensate the change in width.
EP 1 101 721 A1 shows devices for compensating the fanout for the web-fed rotary printing, with which the web is deformed in a wave-shaped pattern at right angles to its direction of conveying before it runs into a next printing gap, in which it is printed on. The width of the web is corrected, i.e., compensated in such a way that it is adapted in advance to the change in width that is to be expected based on the fanout. The present invention also pertains, in particular, to fanout compensators as they are known from EP 1 102 721 A1 and pertains, furthermore, especially also to the fanout compensation processes that can be embodied therewith.
The object of the present invention is to improve the fanout compensation; in particular, the fanout compensation shall not adversely affect the printing process.
The present invention pertains to the fanout compensation in a printing press by means of a fanout compensator, which comprises a rotary body formation, which is wrapped around by a web to be printed on. The wrapping angle should be at least 3xc2x0. A wrapping angle of 5xc2x0 or more, e.g., 10xc2x0, is, however, preferred. The wrapping angle may reach up to 180xc2x0. A wave profile is imposed on the web by the rotary body formation at right angles to the direction of conveying because of the wrapping and the longitudinal tension of the web, which acts in the direction of conveying. The width of the web is reduced by the imposition of the wave profile corresponding to the amplitude of the wave profile in order to compensate the increase in width caused by the fanout. In the best possible approximation, the web should have the same width in the two printing gaps located closest to the fanout compensator in the path of the web, i.e., in the printing gaps between which the fanout compensator is arranged.
According to the present invention, a fluid gap is generated between the surface of the rotary body formation and the web, so that the web has the smallest possible contact area and preferably no direct contact with the rotary body formation at all, but is located at a spaced location from the surface of the rotary body formation corresponding to the thickness of the fluid gap. Frictional forces acting on the web are thus minimized by the fanout compensation, and the longitudinal tension of the web between the printing gaps is advantageously changed much less than in the fanout compensators according to the state of the art. If the underside of the web facing the rotary body formation is printed on with printing ink, the risk that printing ink may be transferred from the underside of the web to the rotary body formation is reduced and, in the ideal case, eliminated.
The fanout compensator according to the present invention comprises a rotary body formation, which has foot sections and head sections, which alternate next to each other along its longitudinal axis and form a wave-shaped surface in order to deform the web to be printed on in a wave-shaped pattern at right angles to the direction of conveying of the web. The foot sections form the wave valleys and the head sections the wave peaks of a wave profile. Fluid channels, which open on the surface of the rotary body formation, are formed in the rotary body formation. The rotary body formation has, furthermore, at least one fluid connection, which is connected to the fluid channels and via which the fluid channels can be supplied with a pressurized fluid. The pressurized fluid introduced via the fluid connection into the fluid channels is guided by the fluid channels to the wave-shaped surface of the rotary body formation and is discharged under pressure on the surface at the opening sites, so that a fluid cushion in the form of the fluid gap is formed between the surface and the underside of the web.
The pressurized fluid is preferably a pressurized gas. Compressed air is especially preferred.
The opening sites of the fluid channels may be arranged distributed uniformly over the surface of the rotary body and uniformly in the circumferential direction. The density of the opening sites per unit area of the surface may, however, vary periodically with the period of the head and foot sections in the axial direction in case of a preferably uniform distribution in the circumferential direction. Thus, the surface density of the opening sites may be greater in the surface sections formed by the head sections than in the surface sections formed by the foot sections in order to compensate axial flows from the head sections into the foot sections.
The fluid channels may be formed as holes and extend from their opening sites on the surface through the head sections and/or foot sections of the rotary body formation radially inwardly into one cavity or optionally into a plurality of cavities, through which they can be or are connected to a fluid source. Such holes may be especially straight and unbranched. Holes may be drilled in the direct sense of the word or they may be prepared by another manner of processing, e.g., by means of laser.
Each of the fluid channels may be separated from each of the other fluid channels and form a single opening site. However, the fluid channels or some of the fluid channels may also branch toward the surface of the rotary body formation and form a plurality of opening sites each there. There may also be cross connections between the fluid channels.
Providing the head sections and/or the foot sections of the rotary body formation with a porosity sufficient for the guiding of the fluid to obtain the fluid channels also corresponds to a preferred embodiment. The porosity is preferably an open porosity, so that the pores of the porous material, which are connected to one another, form the fluid channels. Especially original shaping by compression molding a powder, preferably a metal powder, with subsequent or simultaneous sintering of the molding, is especially suitable for forming porous head sections and/or foot sections. If the foot sections and/or the head sections form fluid channels due to material porosity, holes may also be prepared subsequently, so that the fluid channels are in their entirety partly pore channels and partly holes.
The head sections and foot sections may be formed separately and arranged alternatingly next to each other along the longitudinal axis. Thus, the head sections and the foot sections may be formed, e.g., by rollers, which are mounted rotatably around the longitudinal axis. The head sections may also be mounted rotatably around a common longitudinal axis and the foot sections may likewise be mounted rotatably around a common, other longitudinal axis, and the two longitudinal axes are themselves displaceable in parallel relative to one another for an adjustment of the wave profile of the rotary body formation, as is described especially in EP 1 101 721 A1. In such a design, the head sections and the foot sections would be mounted rotatably around a single, common hollow axle or around two hollow axles that are parallel to each other, through which the fluid can be fed.
However, not least based on the present invention, a rotary mounting of the head and foot sections may be eliminated altogether in such rotary body formations, whose wave profile acting on the web cannot be changed. In particular, it is not necessary for the rotary body formation to be freely rotatable. In particular, the rotary body formation does not have to follow the velocity of the web.
Rotary mounting of the rotary body formation is nevertheless advantageous, namely, to make it possible to adjust the wave profile formed by the surface of the rotary body formation. However, a rotary movement of the rotary body formation takes place in an especially preferred embodiment only for the purpose of adjustment, while the rotary body formation is stopped now in the state set optimally, i.e., is not rotating around its longitudinal axis. Insofar as the longitudinal axis will be called the axis of rotation below in the case of an adjustable rotary body formation, this may also designate, in principle, a rotary body formation mounted freely rotatably around the axis of rotation, but what is meant primarily is a rotary body formation that is rotated around its axis of rotation only for the purpose of adjusting the surface profile formed by it.
In a first embodiment, the rotary body formation is a one-piece rotary body with a rotationally symmetrical surface along the longitudinal axis. The wave profile of this rotary body is not changeable. Even though this rotary body may be mounted freely rotatably around its longitudinal axis, it is preferably mounted nonrotatably in the frame of the printing press. The term xe2x80x9crotary bodyxe2x80x9d is related in the case of the nonrotatable mounting to the preferably round surface of the rotary body and especially preferably to, the surface of the rotary body that is rotationally symmetrical around the longitudinal axis.
In a preferred second embodiment, a rotary body, which forms alternatingly the radially projecting head sections and the radially set-back foot sections next to each other along the longitudinal axis, likewise in one piece, is mounted rotatably around the longitudinal axis in order to change the wave profile formed by the head and foot sections. The features of the one-piece design and adjustability are combined in the second embodiment due to the radial height differences existing between the head sections and the foot sections increasing in the circumferential direction around the axis of rotation from minima, which they have along a first straight line offset in parallel to the axis of rotation, to maxima. The radial height differences have the maxima along a second straight line offset in parallel to the axis of rotation. The first straight line and the second straight line are preferably tangents to all head sections, namely, if all head sections have the same radial height in relation to the axis of rotation. If this is not the case, the two straight lines are the respective tangents to the head section projecting farthest or to the group of head sections projecting farthest. A rotary movement around the axis of rotation, which is uniform for the entire rotary body, is sufficient for the adjustment of the rotary body.
A rotary body according to the second embodiment can also be mounted in a simple manner in the printing press and can be mounted rotatably in the same manner as other rotary bodies of the printing press, e.g., deflecting rollers.
Even though a single, one-piece rotary body preferably forms the entire rotary body formation of the fanout compensator in the first and second embodiments, it shall not be ruled out that a few such rotary bodies, especially two or three rotary bodies or even head and foot sections connected in a torsion-proof manner are arranged next to each other along a common longitudinal axis, which coincides with the axis of rotation in the second embodiment.
The surface of the rotary body formation acting on the web is preferably rounded everywhere in the circumferential direction. The surface may form a circle for this purpose along the longitudinal axis of the rotary body formation, especially everywhere. The surface sections formed by the head sections are preferably arched in a round form radially outwardly in relation to the longitudinal axis, and the surface sections formed by the foot sections are arched in a round form radially inwardly in relation to the longitudinal axis. This is preferably true everywhere over the circumference of the rotary body formation. Furthermore, the head and foot sections should pass over into one another softly on the surface, i.e., they shall be continuously differentiable in the axial direction at the transition sites by passing tangentially over into one another.
Corresponding to a design that is likewise preferred because of its simple manufacturability, the surface sections formed by the head sections are straight in the axial direction over part of their length or over their entire length. The transition sites between the surface sections formed by the foot sections and the head sections should, however, pass softly over into one another over the circumference of the rotary body in this design as well.
A rotary body formation from head sections and foot sections, which are nonrotatable in relation to one another and all or some are formed in preferred embodiments from one or a few rotary bodies in one piece, considerably facilitates the supply of the surface with the pressurized fluid. While a separate rotary fluid connection must be created for each of these head and foot sections in the case of individually rotatably mounted head and foot sections, a common connection is sufficient for the head and foot sections that are not rotatable in relation to one another. Such a connection is preferably created by a hollow axle, on which the head and foot sections that are not rotatable in relation to one another are mounted.
In the case of a nonadjustable rotary body formation, the head and foot sections may be formed each separately and fastened nonrotatably on the hollow axle. However, the head and foot sections are preferably formed in this case in a rotary body in one piece, which has a cavity, e.g., a central hole, of a sufficient length inside in order to supply the entire active surface of the rotary body with the fluid. In an especially preferred second embodiment, in which the wave profile of the rotary body formation acting on the web is changeable, a rotary body, which forms all or some of the head or foot sections in one piece, may be mounted rotatably on the hollow axle. As an alternative, the hollow axle may be replaced by a hollow shaft, i.e., the rotary body forms the bearing journal or the bearing journals for its rotary mounting itself. However, the rotary mounting of the rotary body on a hollow axle, which is mounted itself nonrotatably in the frame of the printing press, is preferred. One advantage of the rotary mounting on a hollow axle is that fluid supply can thus be limited in a simple manner to the part of the waved-shaped surface related to the circumferential direction, which acts on the web.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.